We will continue to direct our efforts to problems concerning the roles of naturally-occurring amino acids in neurotransmission in health and disease. A major concern of the project is the central role of Gamma-aminobutyric acid (GABA) in nervous system function, derangements in the function of which may be involved in various forms of epilepsy, in Huntington's and Parkinson's diseases, and in schizophrenia. We now propose to test the possibility that the nitrogen and carbon for synthesis of glutamate that serves as direct precursor for GABA in presynaptic terminals of immunocytochemically proven GABAergic neurons may arise originally from arginine and ornithine and/or proline. Genetic defects of arginine, ornithine, and proline metabolism in humans all result in mental retardation and/or convulsive seizures. Immunocytochemical marking procedures at the light and electron microscopic levels will employ antisera to the several enzymes involved in the conversion of the above amino acids to glutamate. Further specificity will be added by use of suitable lesioning techniques and appropriate mouse mutants. In vivo operation of suspected pathways will be checked by separate administration of labeled proline, arginine, and ornithine and measurement at various times of concentrations of glutamate and GABA and their isotopic enrichment in order to ascertain whether or not typical precursor-product relations are observed. In related studies, work will continue on the mechanisms of ammonia and hydrazine toxicity and the modes of action of several substances that are protective against one or both of these substances. (Hydrazine is an industrially important neurotoxic substance.) This will include immunocytochemical visualization of adenylic acid deaminase, the enzyme probably responsible for the formation of a large share of the ammonia formed in excitable tissues. Studies in whole animals will be combined with intracellular recordings in hippocampal slices to determine the sites at which the critical effects of both toxic and protective substances are exerted. Particular attention will be given to effects of components of a therapeutic mixture of pure substances, pretreatment with which increases the LD50 of hydrazine in mice almost threefold.